The data transmitted in a packet-switched network (PSN) takes the form of packets processed by switches of the network until they reach their destination. The set of packets transmitted constitutes a data stream.
One technology used to route data packets in packet-switched networks is the multi-protocol label switching (MPLS) technology, which adds to the headers of the data packets one or more labels containing information enabling the routers of the network to determine the next hop that a packet must execute to reach its destination. The MPLS technology is described in more detail in Request For Comments RFC 3031 of the Internet Engineering Task Force (IETF), which is an Internet standardization group.
However, the MPLS protocol can be used to process only packets conforming to the Internet Protocol (IP).
To alleviate this drawback, the virtual circuit concept defined by the IETF PseudoWire Emulation Edge to Edge (PWE3) standardization group enables emulation of a point-to-point connection between two packet-switched network equipments using the IP/MPLS technology. These virtual circuits are also known as pseudo-wires and are defined in the document RFC 3985, and they make it possible to transmit data packets that do not conform to the Internet Protocol, for example data packets conforming to the ATM protocol.
Referring to FIG. 1, a multi-segment pseudo-wire pw1 is set up between a first provider edge node PE1 at the edge of a packet-switched network PSN and a second provider edge node PE2 also at the edge of the PSN. Once the pseudo-wire pw1 has been set up, the first provider edge node PE1 sends a data stream transmitted over the pseudo-wire pw1 to the second provider edge node PE2. The provider edge nodes PE1 and PE2 are routers, Ethernet routers or PW nodes, for example.
The data constituting the data stream sent by the provider edge node PE1 is generated by a first client equipment node CE1 connected to the provider edge node PE1.
The data constituting the data stream received by the provider edge node PE2 is processed by a second client equipment node CE2 connected to the provider edge node PE2.
The provider edge node PE2 encapsulates the data generated by the client equipment node CE2 with a predetermined format. One such format is the data volume, for example. The term data volume refers to the size of the blocks into which the data may be divided, for example blocks of 15 payload bits, or a fixed number of ATM cells that the equipment PE1 is able to receive. The provider edge node PE2 is configured to encapsulate the data according to this predetermined format.
The provider edge node PE1 is also configured to receive data conforming to the predetermined format with which it was encapsulated by the provider edge node PE2.
The pseudo-wire PW1 for transmitting data from the provider edge node PE2 to the provider edge node PE1 is set up at the initiative of the provider edge node PE1 and relies on the exchange of set-up messages conforming to the label distribution protocol (LDP) as defined in the documents RFC 3036 and RFC 4477. Accordingly, a first pseudo-wire set-up message is sent by the provider edge node PE1 to a router S-PE of the network PSN to set up a first link L1 of the pseudo-wire pw1. This first set-up message includes an identifier SAII1 of the source provider edge node PE1, an identifier TAII2 of the terminating provider edge node PE2, parameters of the pseudo-wire, and a first label that is added to the header of all the data sent by the router S-PE to the provider edge node PE1 through the first link of the pseudo-wire pw1.
A second link L2 of the pseudo-wire pw1 is set up between the router S-PE and the second provider edge node PE2. The router S-PE sends the second provider edge node PE2 a second set-up message that includes an identifier SAII1 of the provider edge node PE1, an identifier TAII2 of the provider edge node PE2, parameters of the pseudo-wire, and a second label that is added to the header of all the data sent by the second provider edge node PE2 to the router S-PE through the second link of the pseudo-wire pw1.
On reception of the pseudo-wire set-up message, the provider edge node PE2 sends the router S-PE a third pseudo-wire set-up message including an identifier SAII2 of the provider edge node PE2, an identifier TAII1 of the provider edge node PE1, parameters of the pseudo-wire, and a third label that is added to the header of all the data sent by the router S-PE to the provider edge node PE2 through the second link of the pseudo-wire pw1.
The router S-PE sends the first provider edge node PE1 a fourth pseudo-wire set-up message including an identifier SAII2 of the provider edge node PE2, an identifier TAII1 of the provider edge node PE1, parameters of the pseudo-wire, and a fourth label that is added to the header of all the data sent by the first provider edge node PE1 to the router S-PE through the first link of the pseudo-wire pw1.
Once the pseudo-wire pw1 has been set up between the provider edge node PE1 and the provider edge node PE2, it transmits data bidirectionally between the provider edge node PE1 and the provider edge node PE2. Pseudo-wires such as the pseudo-wire pw1 are defined in detail in the document “An Architecture for Multi-Segment Pseudo-Wire Emulation Edge-to-Edge (draft-ietf-pwe3-ms-pw-arch-02.txt)”.
In this instance, the client equipment node CE1 connected to the provider edge node PE1 is adapted to process data generated by the client equipment node CE2 connected to the provider edge node PE2.
The pairs {provider edge node PE1 identifier SAII1/provider edge node PE2 identifier TAII2} and {provider edge node PE2 identifier SAII2/provider edge node PE1 identifier TAII1} constitute two forwarding equivalence classes (FEC) each of which defines one transmission direction of the same pseudo-wire pw1.
To increase the bit rate of a pseudo-wire, the telecommunication provider managing the PSN has to modify the format of the data transmitted through the pseudo-wire pw1. Two solutions are available for this.
A first solution consists in destroying the pseudo-wire pw1 and setting up a new pseudo-wire adapted to transmit data conforming to the new format.
FIG. 2 is a diagram representing the exchange of messages between the provider edge node PE1, the router S-PE, and the provider edge node PE2 when this solution is used.
When the data format is changed in the first client equipment node CE1, said equipment informs the provider edge node PE1 of this. The provider edge node PE1 then sends the router S-PE a message LWM1 requesting release of the resources used by the first link L1 of the pseudo-wire pw1 in the uplink direction, i.e. from the router S-PE to the provider edge node PE1. On reception of this message LWM1, the router in turn sends the provider edge node PE2 a message LWM1′ requesting release of the resources used by the second link L2 of the pseudo-wire pw1 in the uplink direction, i.e. from the provider edge node PE2 to the router S-PE.
On reception of the message LWM1′, the provider edge node PE2 in turn sends the router S-PE a message LWM2 requesting release of the resources used by the second link L2 of the pseudo-wire pw1 in the downlink direction, i.e. from the router S-PE to the second provider edge node PE2. On reception of this message LWM2, the router S-PE in turn sends the provider edge node PE1 a message LWM2′ requesting release of the resources used by the first link L1 of the pseudo-wire pw1 in the downlink direction, i.e. from the provider edge node PE1 to the router S-PE.
On reception of the message LWM2′, the provider edge node PE1 sends the router S-PE a first message LMM1 to set up a new pseudo-wire. On reception of the set-up message LMM1, the router in turn sends the provider edge node PE2 a second set-up message LMM1′.
On reception of the message LMM1′, the provider edge node PE2 sends a third set-up message LMM2 to the router S-PE. On reception of the set-up message LMM2, the router in turn sends the provider edge node PE1 a fourth set-up message LMM2′.
The set up messages LMM1, LMM1′, and LMM2, LMM2′ of the new pseudo-wire each include an FEC for identifying the new pseudo-wire and new parameters of the pseudo-wire, for the uplink direction in the messages LMM1 and LMM1′ and for the downlink direction in the messages LMM2 and LMM2′. Accordingly, the new pseudo-wire set up is able to transmit data conforming to the new format for each transmission direction.
When it is implemented, a solution of the above kind requires interruption of the data packet traffic between the provider edge node PE1 and the provider edge node PE2. Depending on the nature of the data routed by the pseudo-wire, such interruption of the traffic degrades quality of service, especially if the data routed is real-time data.
A second solution, represented in FIG. 3, consists in setting up a second pseudo-wire pw2 between the provider edge node PE1 and the provider edge node PE2. The elements of this figure already described with reference to FIG. 1 carry the same references and are not described again.
The set up messages of the pseudo-wire pw2 in the uplink direction and in the downlink direction each include an FEC different from the corresponding FEC identifying the pseudo-wire pw1 and the new parameters of the new pseudo-wire pw2.
In this solution, a new pseudo-wire must be set up between the provider edge node PE1 and the provider edge node PE2 on each modification of the format of the data with a view to modifying the bit rate of a pseudo-wire.
Although making it possible to ensure continuity of service, such a solution has the drawback of being greedy for network resources, for example processing resources in the equipments (storage capacity, calculation capacity, etc.).
The solution proposed by the invention does not have the drawbacks of the prior art solutions.